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Java设计模式研究之Flyweight模式

 2008-01-05 09:44:10 来源:WEB开发网   
核心提示:GOF:运用共享技术有效地支持大量细粒度的对象, 解释一下概念:也就是说在一个系统中假如有多个相同的对象,Java设计模式研究之Flyweight模式,那么只共享一份就可以了,不必每个都去实例化一个对象,此时变量flyweight为null,产生一个新的flyweight存储在Hashtable中,比如说(这里引用GO

  GOF:运用共享技术有效地支持大量细粒度的对象。

  解释一下概念:也就是说在一个系统中假如有多个相同的对象,那么只共享一份就可以了,不必每个都去实例化一个对象。比如说(这里引用GOF书中的例子)一个文本系统,每个字母定一个对象,那么大小写字母一共就是52个,那么就要定义52个对象。假如有一个1M的文本,那么字母是何其的多,假如每个字母都定义一个对象那么内存早就爆了。那么假如要是每个字母都共享一个对象,那么就大大节约了资源。

  在Flyweight模式中,由于要产生各种各样的对象,所以在Flyweight(享元)模式中常出现Factory模式。Flyweight的内部状态是用来共享的,Flyweight factory负责维护一个对象存储池(Flyweight Pool)来存放内部状态的对象。Flyweight模式是一个提高程序效率和性能的模式,会大大加快程序的运行速度.应用场合很多,下面举个例子:

  先定义一个抽象的Flyweight类:

package Flyweight;

public abstract class Flyweight
...
{
 public abstract void Operation();
}//end abstract class Flyweight
  在实现一个具体类:

package Flyweight;

public class ConcreteFlyweight extends Flyweight
...
{
 PRivate String string;
 public ConcreteFlyweight(String str)
 ...
 {
  string = str;
 }//end ConcreteFlyweight(...)

 public void operation()
 ...
 {
  System.out.println("Concrete---Flyweight : " + string);
 }//end operation()

}//end class ConcreteFlyweight
  实现一个工厂方法类:

package Flyweight;
import java.util.Hashtable;

public class FlyweightFactory
...
{
 private Hashtable flyweights = new Hashtable();//----------------------------1
 public FlyweightFactory() ...{}

 public Flyweight getFlyWeight(Object obj)
 ...
 {
  Flyweight flyweight = (Flyweight) flyweights.get(obj);//----------------2

  if(flyweight == null) ...{//---------------------------------------------------3
   //产生新的ConcreteFlyweight
   flyweight = new ConcreteFlyweight((String)obj);
   flyweights.put(obj, flyweight);//--------------------------------------5
  }
  return flyweight;//---------------------------------------------------------6
 }//end GetFlyWeight(...)

 public int getFlyweightSize()
 ...
 {
  return flyweights.size();
 }
}//end class FlyweightFactory
  这个工厂方法类非常要害,这里具体解释一下:

  在1处定义了一个Hashtable用来存储各个对象;在2处选出要实例化的对象,在6处将该对象返回,假如在Hashtable中没有要选择的对象,此时变量flyweight为null,产生一个新的flyweight存储在Hashtable中,并将该对象返回。

  最后看看Flyweight的调用:

package Flyweight;
import java.util.Hashtable;

public class FlyweightPattern ...{
 FlyweightFactory factory = new FlyweightFactory();
 Flyweight fly1;
 Flyweight fly2;
 Flyweight fly3;
 Flyweight fly4;
 Flyweight fly5;
 Flyweight fly6;

 /** *//** Creates a new instance of FlyweightPattern */
 public FlyweightPattern() ...{
  fly1 = factory.getFlyWeight("Google");
  fly2 = factory.getFlyWeight("Qutr");
  fly3 = factory.getFlyWeight("Google");
  fly4 = factory.getFlyWeight("Google");
  fly5 = factory.getFlyWeight("Google");
  fly6 = factory.getFlyWeight("Google");
 }//end FlyweightPattern()

 public void showFlyweight()
 ...
 {
  fly1.operation();
  fly2.operation();
  fly3.operation();
  fly4.operation();
  fly5.operation();
  fly6.operation();
  int objSize = factory.getFlyweightSize();
  System.out.println("objSize = " + objSize);
 }//end showFlyweight()

 public static void main(String[] args)
 ...
 {
  System.out.println("The FlyWeight Pattern!");
  FlyweightPattern fp = new FlyweightPattern();
  fp.showFlyweight();
 }//end main(...)
}//end class FlyweightPattern
  下面是运行结果:


Tags:Java 设计模式 研究

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